Process for bleaching



Tllciiv UNITED STATES PATENT OFFICE PROCESS FOR BLEACHING Ehrhart Franz, Leipzig, Germany No Drawing. Application February 23, 1934, Serial No. 712,608. In Germany January 18,

7 Claims.

This invention relates to a process of bleaching organic material by means of bleaching agents which give off oxygen.

In respect to a combined action of stabilizers and activators, and to a continuous bleaching process,as suggested herein,see my two 00- pending applications-Bleaching process, Ser. No. 710,527, filed February 9, 1934, and Continuous bleaching process, Ser. No. 712,609, filed February 23, 1934, respectively.

Bleaching agents of this class comprise especially hydrogen peroxide and the oxygen-yielding acids of organic or inorganic origin as well as the salts thereof, such as the percarbonates, perphosphates, permonosulfuric acids. Such compounds have been used for a long time for bleaching organic materials including both natural materials obtained from animals or plants and artificial ones. Bleaching is highly important for the seed hairs or the fruits or fibers, such as cotton, nettle, jute, hemp, legumes, cereals and others, or for W001, silk, skin, horn, teeth, hairs, or for artificial silk, artificial resin and the like. If the bleaching agents mentioned are used in the customary manner in an alkaline medium, i. e., as solutions possessing a high pH-value, a good bleaching effect will be attained, but the bleaching liquor activated by the high pH-value will lose spontaneously by far the greatest part of its oxygen which thus will not participate in the bleaching and will not be utilized. On the other hand, if, as has been proposed already, bleaching solutions stabilized by the addition of acids, i. e., solutions having a low pH-value, are used, it is believed that by continuing the action for a long time a favorable bleaching effect can be attained, though, as a matter of fact, the effect does not improve with time but gradually deteriorates, since under the influence of the bleaching agent and the acid yellowing will take place as a side reaction. Furthermore, the loss of material in such a bath is greater than in a solution of high pH-value, particularly if the bath acts for a longer period. Acid bleaching has thus not been found satisfactory, and for this reason bleaching has, as a rule, been carried out in an alkaline liquor.

The invention proposes an improvement over existing methods by providing that the liquor is to act only until the most favorable bleaching effect is attained. It is therefore necessary to ascertain by tests or observation when the side reaction or yellowing begins to take place in bleaching. The invention is based on the knowledge that in a bleaching solution having a low pH-value, i. e., in a stabilized solution, bleaching is effected unexpectedly in a very rapid way, but that after a short time a side reaction will set in also which causes the material to turn reddishyellow. When bleaching is stopped after the most favorable effect has been attained, absolutely pure while effects are sometimes not produced to be sure, but the material is hardly affected and bleaching can be easily completed in other ways. For this final bleaching hydrogen peroxide liquor may be used beside other baths. It has been found that inorganic acids in particular, with the exception of phosphoric and boric acids, tend to accelerate the appearance of yellowing, whereas the great majority of organic acids behaves favorably. Therefore, if unsuitable acids are concerned, the salts of suitable weaker acids are preferably added. For example, if phosphoric or oxalic acids are used or phosphates or oxalates are added, the beginning of yellowing is retarded in such a way that bleaching effects are attained which are not inferior to those produced in an alkaline bath. This result is obtainable practically without attacking the material to be' bleached and while saving and utilizing the bleaching agent to the utmost. The saving effect with respect to the material becomes apparent particularly during the bleaching of material of animal origin, such as wool, which is known to be especially sensitive to alkalies. In order to further shorten the acting period of the bleaching liquor it is advisable to accelerate catalytically the bleaching process, since it has been found that yellowing is far less accelerated thereby than bleaching. Such acceleration is preferably effected by impregnating the material to be bleached with substances activating the bleaching process, e. g., substances capable of imparting a high pH-value to their aqueous solution like alkali hydroxide, alkali carbonate, trialkali phosphate, alkali pyrophosphate, soap or the like, or by applying salts of heavy metals or of enzymes or ferments. When substances having an alkaline reaction are to be used they may be left in the material from the preparatory treatment, or such compounds may be applied prior to bleaching. Enzymes are found, as a rule, in the raw material, so that it is only necessary to prevent their complete removals from the material subjected to bleaching. If the material contains much activator, care should be taken to prevent the latter from passing into the bath, and bleaching in this case is preferably carried out so that the material to be bleached is merely impregnated. Impregnation can be effected by sup placing the material into a bath for a short time only and then squeezing it out or centrifuging it or spraying on the bleaching liquor. Bleaching is then preferably completed by storing the material in wet condition at room temperature or at a slightly higher temperature and possibly drying it at the same time. In such a case the use of several baths may be advisable, a bath having a low content of bleaching agents being used to start with. The process according to the invention may further be employed as a step in a combination bleaching process, and preceded or followed by other processes or liquors. As stated before, it is possible to employ the process successfully for preliminary bleaching and complete bleaching in an alkaline bath while using the same bleaching agent.

It may be pointed out that the use of a stabilized bath is of course not a preliminary condition and that, with equal success, stable, i. e., not activated baths or solutions, may be employed. It has been ascertained that a pH-range of 3 to 8 is particularly suitable for carrying out the bleaching.

The following examples are intended to explain the invention which, however, is not restricted to them:

Example 1 Cotton is steeped in the usual way in an alkaline bath in the presence of 0.03% sodium hydrosulphite formaldehyde, then shortly rinsed, whereupon the goods which still react in alkaline fashion are placed in bleaching liquor consisting of 5 parts by weight of hydrogen peroxide per liter stabilized by the addition of 0.03% phosphorlc acid. Bleaching is preferably carried on between and 60 C. until the optimum has been attained when the goods are instantly removed from the bath and washed as usual.

Instead of phosphoric acid sulphuric acid may be employed, in which case some sodium sulphate, approximately 0.2%, is added. Oxalic acid also can be used as stabilizer as can isobutyl naphthalene sulfonic acid or boric acid. If so dium perborate is used instead of hydrogen peroxide in preparing the bleaching liquor a somewhat larger amount of acid is needed, but the bleaching period is hardly prolonged thereby.

Example 2 100 parts by weight of jute are preliminarily bleached with 800 parts by volume of bleaching solution, which is obtained from 1 part by weight of chloride of lime by conversion with soda solution containing 0.6 part by weight of calcined soda, at room temperature for 12 to 14 hours. Then rinsing takes place in the usual way while some thiosulphate is added in the beginning, whereupon a 0.5% oxalic acid solution is used for acidification lasting a very short time. The goods will then still react clearly in alkaline manner on litmus paper. Bleaching is then completed in a liquor having a content of 0.5% to 1% of hydrogen peroxide stabilized by 0.1% sulphuric acid while adding a small amount of aluminium sulphate if necessary. The goods are then left for about half an hour in the bath at room temperature and later on stored while wet at a moderately increased temperature until the best bleaching effect has been attained. They are then shortly rinsed and dried.

If the pre-treated goods are acidified with oxalic or phosphoric acid so that the material to be bleached shows already acid reaction, ac-

celeration of bleaching can advantageously be attained after the application of the stabilized bleaching solution by specially treating the material with an activating bath, such as ammonia.

Instead of sulphuric acid, phosphoric acid, isobutyl naphthalene sulfonic acid, cetyl alcohol sulfonic acid, the sulfo acid of octadecenol sulphuric acid ester, stearyl alcohol phosphoric acid, oleomethylaminoethane sulfo acid and other acids or the salts thereof can be used. The aluminium salt can for instance be replaced by a magnesium salt. To attain a perfectly clear white a third bleaching bath may be resorted to, preferably prepared from 0.1% sodium hyposulphite, 0.1% calcined soda and 0.1% olein soap. Bleaching is continued for about 20 minutes at approximately 95.

Example 3 Jute is freed from dust and then placed in a bath containing 0.5% commercial hydrogen peroxide. The goods remain in the bath for several hours, and the enzymes in the raw jute will bring it about that the otherwise quite inert bleaching solution will produce a yellowish white material which is then put into a bath of about 3% hydrogen peroxide stabilized by the addition of sodium bioxalate, and left therein at room temperature until the best white effect has been attained.

Stabilization of the first bath is not required, since such low-percentage solutions are stable per se. Stabilization of the second bath can take place also by other compounds of low pH-value or by colloids, such as silicic acid gel, or by phenols, amines or the like.

Example 4 100 parts by weight of animal hair, such as Angora goats hair or sheeps wool, are washed in the usual way with soap and water and thoroughly rinsed, though the animal hair will retain about 1% soap. Having been worked into tops the material is placed for 2 to 10 minutes in a bath of 0.5% hydrogen peroxide and 0.03% oxalic acid whose temperature is to 40 C. when the best bleaching efiect is attained. The material is then centrifuged or squeezed and dried for some time at lower or a short time at higher temperatures by passing it for instance over heated rolls.

A feature of this process is that the animal material is damaged only very slightly and the loss in weight in particular is quite negligent.

Example 5 100 parts by weight of hat bodies mordanted as usual with mercury salts are placed in 600 parts of a. bleaching bath of 3% hydrogen peroxide and 1% magnesium sulfate and then stored while wet. The bleaching bath has been stabilized by means of 0.1% to 0.2% lactic acid or phosphoric acid, and bleaching up to the best efiect requires about 3 hours at 40 to 50 and up to 24 hours at room temperature. During this time the acid content of the bath must be corrected at inter vals to maintain the standard mentioned.

Example 6 100 parts by weight of wool in top form are placed in 600 parts of a bath of 1% potassium permanganate, which has been slightly acidified by sulphuric acid or to which about 1% magnesium sulfate has been added, for 30 minutes at room temperature. The wool will then be dyed brown by separated manganese dioxide hydrate. It is rinsed thoroughly and then placed in a bath containing 1% to 2% hydrogen peroxide and 0.2% sulphuric acid and 0.5% to 1% magnesi- 5 um sulfate or sodium oxalate for about minutes at 30 to 40 C., whereupon the same amount of sulphuric acid or a corresponding amount of sodium sulfate is added. Bleaching will be completed after about 10 to 30 minutes when the 10 goods are thoroughly rinsed and cleared in a bisulphate bath with about 1% sodium bisulphite and 0.6% sulphuric acid. To attain a white of greatest purity and durability it is advisable to add a sodium hydrosulphite bath containing about 0.1% to 0.3% sodium hydrosulphite. Bleaching is continued for about 3 to 6 hours at approximately 35 to 40 C., whereupon rinsing and acidification take place in the usual way.

The pH value of the bleaching solutions of the 2 foregoing examples ranges between 4.5 and 6.5.

While I have determined that such range generally yields the best results, more or less acid activities may be used under particular circumstances.

25 I claim:-

1. In a chlorine-free bleaching process, the step of acid bleaching in a hydrogen peroxide solution rendered acid by an addition selected from the group consisting of sulphuric acid in combination with an alkaline sulphate, boric acid, phosphoric acid, and the organic acids.

2. The process as claimed in claim 1, according to which the solution of bleaching agents has a pH value above 3.

3. The process as claimed in claim 1, according to which the solution 01' bleaching agents has a pH value of 4.5 to 6.5.

4. The process as claimed in claim 1, according to which the material to be bleached carries at the points to be bleached activators accelerating bleaching and alkaline in the presence of water.

5. The process as claimed in claim 1, according to which the material to be bleached carries at the points to be bleached enzymes for activating bleaching.

6. The process as claimed in claim 1, according to which oxalate ions are present in the bath for repressing yellowing.

7. As a chlorine-free bleaching medium, an acid solution containing hydrogen-peroxide, and a weak acid addition selected from the group consisting of sulphuric acid in combination with a sulphate of alkaline reaction, boric acid, phosphoric acid, and the organic acids, the nature of these additions retarding the yellowing of the material to be bleached.

EHRHART FRANZ. 

